Rear suspension structure for motorcycle

Abstract

 A left arm portion (75) and a right arm portion (76) which extend in the front-rear direction are provided on the left and right sides of a swing arm (24), a window portion for passing a rear cushion unit (28) therethrough is provided between the left arm portion (75) and the right arm portion(76), a cushion-fitting beam (31) is bridgingly provided between the left arm portion (75) and the right arm portion (76), a swing arm side fitting portion(61)of the rear cushion unit (28) is fitted to the cushion-fitting beam (31), and the whole part or a part of the window portion is closed with the cushion-fitting beam (31).
The swing arm (24) can be reinforced with the cushion-fitting beam (31), and the flexural rigidity and torsional rigidity of the swing arm (24) can be enhanced. Moreover, since the upper end (61) of the cushion unit (28) is fitted to the swing arm side, it is unnecessary to provide, for example, a fitting portion for the upper end (61) of the cushion unit (28) on the vehicle body frame side, so that an increase in weight can be restrained.

Description

[0001] The present invention relates to a rear suspension structure for motor cycle which is suitable for enhancing the rigidity of a swing arm while restraining an increase in the weight of a vehicle body.

[0002] As a rear suspension structure for motor cycle, there is generally a structure in which a swing arm is extended from the vehicle body side toward the rear side of the vehicle body, and end portions of a rear cushion unit are fitted to the swing arm and to the vehicle body side. This technology will be described referring to Fig. 10.
   Fig. 10 is a side view of a major part for illustrating a conventional rear suspension structure, and shows a structure in which respective rear portions of left and right main frames 301, 301 (the main frame 301 on the deep side is not shown) constituting a vehicle body frame 300 are connected to each other by an upper portion cross pipe 302 and a lower portion cross pipe 303, the upper portion cross pipe 302 is provided with a bracket portion 304 projecting rearwards, an upper end portion of a rear cushion unit 306 is fitted to the bracket portion 304, and a lower end portion of the rear cushion unit 306 is fitted to a lower portion of a swing arm 308 through a link 307. The link 307 is fitted to a lower portion of the lower portion cross pipe 303 through a link 311.
   The swing arm 308 is a member provided with a cushion inserting hole 313 for passing the rear cushion unit 306 therethrough.

[0003] In the above technology, the swing arm 308 is provided with the cushion inserting hole 313 for the rear cushion unit 306, so that the flexural rigidity and torsional rigidity of the swing arm 308 are reduced due to the presence of the cushion inserting hole 313, which is considered to affect drivability and stability at the time of cornering, for example.
   However, the measure of increasing the size of the swing arm 308 or merely fitting a reinforcement member to the swing arm 308 would increase the weight of the vehicle body or impair the motion performance of the vehicle.

[0004] Accordingly, it is an object of the present invention to enhance the rigidity of the swing arm while restraining an increase in the weight of the vehicle body, by improving the rear suspension structure for motorcycle.

[0005] In order to attain the above object, claim 1 is characterized in that, in a rear suspension structure including a swing arm having one end swingably fitted to a pivot shaft provided on the vehicle body side, a wheel fitted to the other end of the swing arm, and a cushion unit having an upper end fitted to the swing arm, the lower end of the cushion unit connected to the vehicle body side, arm portions extending in the front-rear direction are provided on the left and right sides of the swing arm, a window portion for passing the cushion unit therethrough is provided between the arm portions, a cross beam is bridgingly provided between the arm portions, the upper end of the cushion unit is fitted to the cross beam, and the whole part or a part of the window portion is closed with the cross beam.

[0006] Since the whole part or a part of the window portion of the swing arm is closed with the cross beam, the swing arm can be reinforced by the cross beam, and the flexural rigidity and torsional rigidity of the swing arm can be enhanced. Moreover, since the upper end of the cushion unit is fitted to the swing arm side, it is unnecessary to provide, for example, a fitting portion for the upper end of the cushion unit on the vehicle body frame side, and, therefore, an increase in weight can be restrained.

[0007] The rear suspension structure for motorcycle as set forth in claim 1 is the rear suspension structure including the swing arm having one end swingably fitted to the pivot shaft provided on the vehicle body side, the wheel fitted to the other end of the swing arm, and the cushion unit having the upper end fitted to the swing arm, the lower end of the cushion unit being connected to the the front-rear direction are provided on the left and right sides of the swing arm, the window portion for passing the cushion unit therethrough is provided between the arm portions, the cross beam is bridgingly provided between the arm portions, the upper end of the cushion unit is fitted to the cross beam, and the whole part or a part of the window portion is closed with the cross beam. Therefore, the swing arm can be reinforced by the cross beam, and the flexural rigidity and torsional rigidity of the swing arm can be enhanced. Moreover, since the upper end of the cushion unit is fitted to the swing arm side, it is unnecessary to provide, for example, a fitting portion for the upper end of the cushion unit on the vehicle body frame side, so that an increase in weight can be restrained.

[0008] Claim 2 is characterized in that the cross beam is trapezoid shaped in front view, and the upper end of the cushion unit is fitted to the upper side of the cross beam.

[0009] Since the cross beam is trapezoid shaped in front view, vertical forces exerted on the cross beam upon extension or contraction of the cushion unit can be received roughly as a tensile force or a compressive force by slant sides of the trapezoid-shaped cross beam.

[0010] For example, where the cross beam is included of a straight member and the spacing between left and right arm portions of the swing arm is wide, the cross beam becomes longer, and a greater flexural moment is generated in the cross beam. In contrast, according to the present invention, the flexural moment can be decreased, and the rigidity of the cross beam against the extension and contraction of the cushion unit can be enhanced.

[0011] The rear suspension structure for motorcycle as set forth in claim 2 is a structure in which the cross beam is trapezoid shaped in front view, and the upper end of the cushion unit is fitted to the upper side of the cross beam. Therefore, when a vertical force is exerted on the beam due to extension or contraction of the cushion unit, the vertical force can be received roughly as a tensile force or a compressive force by the slant sides of the trapezoid-shaped cross beam.

[0012] For example, where the cross beam is included of a straight member and the spacing between the left and right arm portions of the swing arm is wide, a larger flexural moment is generated. In contrast, according to the present invention, the flexural moment can be reduced, so that the rigidity of the cross beam against extension and contraction of the cushion unit can be enhanced.

[0013] Therefore, it is unnecessary to enlarge the cross sectional area of the cross beam or to specially reinforce the cross beam, so that the cross beam can be made smaller in weight, and production costs of the cross beam and the rear suspension device can be reduced.

[0014] Claim 3 is characterized in that the fitting of the upper end of the cushion unit to the swing arm and the fitting of the lower end of a rear cushion unit to the vehicle body side are performed respectively through spherical sliding bearings.

[0015] By fitting the upper end and the lower end of the cushion unit through the spherical sliding bearings, inclinations of the cushion unit with reference to the swing arm side and the vehicle body side can be absorbed, so that excessive external forces can be prevented from acting on the cushion unit itself, on the swing arm side or on the vehicle body side.

[0016] The rear suspension structure for motorcycle as set forth in claim 3 is a structure in which the fitting of the upper end of the cushion unit to the swing arm and the fitting of the lower end of the cushion unit to the vehicle body side are performed respectively through spherical sliding bearings. Therefore, the inclinations of the cushion unit relative to the swing arm side and the vehicle body side can be absorbed, and excessive external forces can be prevented from acting on the cushion unit itself, the swing arm side or the vehicle body side.

[0017] A mode for carrying out the present invention will be described below based on the accompanying drawings, in which:

Fig. 1 is a side view of a major portion of a motorcycle adopting a rear suspension structure according to the present invention.

Fig. 2 is a side view of a major portion for illustrating the rear suspension structure according to the present invention.

Fig. 3 is a sectional view taken along line 3-3 of Fig. 2.

Fig. 4 is an enlarged view of portion A of Fig. 3.

Fig. 5 is an enlarged view of portion B of Fig. 3.

Fig. 6 is a plan view of a swing arm in the rear suspension structure according to the present invention.

Fig. 7 is a first action view for illustrating the action or effects of the rear suspension structure according to the present invention.

Fig. 8 is a second action view for illustrating the action or effects of the rear suspension structure according to the present invention.

Fig. 9 is a third action view for illustrating the action or effects of the rear suspension structure according to the present invention.

Fig. 10 is a side view of a major portion of illustrating a conventional rear suspension structure.

[0018] The drawings are to be looked at in accordance with the posture of symbols.
   Fig. 1 is a side view of a major part of a motorcycle adopting a rear suspension structure according to the present invention. The motorcycle 10 is a vehicle which includes a vehicle body frame 14 including a left-right pair of main frames 12, 12 (the main frame 12 on the deep side is not shown) extended rearwardly downwards from a head pipe 11, and pivot brackets 13, 13 (the pivot bracket 13 on the deep side is not shown) as the vehicle body side fitted to rear portions of the main frames 12, 12, and in which a rear suspension device 15 according to the present invention is fitted to the pivot brackets 13, 13.

[0019] Numeral 16 denotes a V-type engine including a front-side cylinder 16a and a rear-side cylinder 16b, which is fitted to respective engine-fitting portions 17, 18 of the main frames 12, 12 and respective engine-fitting portions 21, 22 of the pivot brackets 13, 13.

[0020] Numeral 24 denotes a swing arm, which is swingably fitted to a pivot shaft 25 bridgingly provided between the pivot brackets 13, 13, and a rear wheel 26 as a wheel is fitted to the rear end of the swing arm 24.

[0021] Numeral 28 denotes a rear cushion unit, of which the upper end is fitted to a cushion-fitting beam 31 as a cross beam fitted to an upper portion of the swing arm 24, and the lower end is fitted to a lower portion bracket 33 provided at a lower portion of the swing arm 24 through a first link 32, and the first link 32 is fitted to the lower ends of the pivot brackets 13, 13 through a second link 34.

[0022] Numeral 36 denotes an intake box which is for once reserving air for supplying air to the engine 16 and which is fitted to upper portions of the main frames 12, 12.
   Numeral 37 denotes a fuel tank, which is disposed on the upper side of the main frames 12, 12 and on the rear side of and in proximity to the intake box 36.

[0023] Numeral 41 denotes a rear fender of which a front portion is fitted to cowl-fitting portions 42, 43 provided respectively at upper portions of the main frames 12, 12, and which covers the upper side of a rear portion of the fuel tank 37, and further covers the upper side of the rear wheel 26, with a seat 44 fitted to an upper surface of the rear fender. 41 corresponding to the upper side of a rear portion of the fuel tank 37.

[0024] Here, numeral 45 denotes a front fork steerably fitted to the head pipe 11, 46 denotes a front wheel fitted to the lower end of the front fork 45, 47 and 48 denote hanger portions provided on the side of the engine 16 for fitting the engine 16 to the main frames 12, 12, 51 and 52 denote hanger portions provided on the side of the engine 16 for fitting the engine 16 to the pivot brackets 13, 13, 53 denotes an oil pan provided at a lower portion of the engine 16, 54 denotes a fuel pump provided in the fuel tank 37, and 55 denotes a back rest provided on the rear fender 41 on the rear side of the seat 44.

[0025] Fig. 2 is a side view of a major part for illustrating the rear suspension structure according to the present invention. The rear cushion unit 28 includes a cylinder portion 57 filled with an oil, a piston 58 movably inserted in the cylinder portion 57, a piston rod 59 fitted to the piston 58, a swing arm side fitting portion 61 (namely, the upper end of the cushion unit described in claim 1) provided at an end portion of the cylinder portion 57 for fitting to the cushion-fitting beam 31 of the swing arm 24, a link side fitting portion 62 (namely, the lower end of the cushion unit described in claim 1) provided at an end portion of the piston rod 59 for fitting to the first link 32, and a spring 63 intermediately provided between the swing arm side fitting portion 61 and the link side fitting portion 62. Numeral 64 denotes a reservoir tank for reserving the oil flowing out from the cylinder portion 67 upon thermal expansion of the oil contained in the cylinder portion 57.

[0026] The first link 32 is fitted with three support shafts 65, 66, 67; the first link 32 is swingably fitted to the lower portion bracket 33 through the support shaft 65, the first link 32 is swingably fitted to the rear cushion unit 28 through the support shaft 66, and the second link 34 is swingably fitted to the first link 32 through the support shaft 67.

[0027] The second link 34 is swingably fitted, through a support shaft 72, to two link-fitting portions 71, 71 (the link-fitting portion 71 on the deep side is not shown) provided on a cross beam 68 connecting the respective lower ends of the pivot brackets 13, 13.

[0028] Fig. 3 is a sectional view taken along line 3-3 of Fig. 2, and shows the condition where the trapezoid-shaped cushion-fitting beam 31 is fitted by bolts 77, 77 to respective upper portions of a left arm portion 75 and a right arm portion 76 disposed on the left and right sides of the swing arm 24 and extended in the longitudinal direction, the swing arm side fitting portion 61 of the rear cushion unit 28 is screw-connected to a cushion-fitting portion 31c as the upper side of the cushion-fitting beam 31, and the link side fitting portion 62 of the rear cushion unit 28 is fitted to the first link 32. Numeral 81 denotes a lock nut for fixing the swing arm side fitting portion 61 to the cushion-fitting beam 31.

[0029] The cushion-fitting beam 31 includes base portions 31a, 31a for fitting to the swing arm 24, inclined portions 31b, 31b skewly rising to the inner upper side from the base portions 31a, 31a, and the above-mentioned cushion-fitting portion 31c for connecting respective upper portions of the inclined portions 31b, 31b and for fitting the rear cushion unit 28.

[0030] Fig. 4 is an enlarged view of portion A of Fig. 3. The swing arm side fitting portion 61 of the rear cushion unit 28 includes a tubular case 83 screw-connected to the cushion-fitting beam 31, an outer ring 84 contained in the case 83, an outer ring fixing nut 86 screw-connected to the inside surface of the case 83 for fixing the outer ring 84 in the case 83, an inner ring 87 sliding on the inside surface of the outer ring 84, and an inner ring fixing bolt 91 for fixing the inner ring 87 to an end portion of the cylinder portion 57 through a spacer 88.

[0031] The above-mentioned outer ring 84 has a structure in which the inside surface of a tubular member is formed as a part of a concave spherical surface and outer ring halves 84a, 84a of the same shape are disposed adjacent to each other, whereas the inner ring 87 has a structure in which the outside surface of a tubular member is formed as a part of a convex spherical surface.
   The outer ring 84 and the inner ring 87 constitute a spherical sliding bearing 93.

[0032] Fig. 5 is an enlarged view of portion B of Fig. 3. The link side fitting portion 62 of the rear cushion unit 28 includes an outer ring 95 fitted to the side of the piston rod 59 (See Fig. 2), an inner ring 96 sliding on the outside surface of the outer ring 95, spacers 97, 97 clamping the inner ring 96 therebetween and disposed on the inside of the first link 32, a bolt 98 penetrating through the inner ring 96, the spacers 97, 97 and the first link 32 for fastening the portion between the first links 32, and a nut 99 screw-connected to the tip end of the bolt 98.
   The outer ring 95 and the inner ring 96 constitute a spherical sliding bearing 101.

[0033] Fig. 6 is a plan view of the swing arm in the rear suspension structure according to the present invention. The swing arm 24 is a member which includes a left arm portion 75 and a right arm portion 76 extending in the longitudinal direction, a front portion connecting portion 103 and an intermediate portion connecting portion 104 for connection between the left arm portion 75 and the right arm portion 76, a window portion 106 provided for passing the rear cushion unit 28 therethrough between the front portion connecting portion 103 and the intermediate portion connecting portion 104, and pivot shaft support portions 107, 107 for supporting the pivot shaft 25 (See Fig. 2), and in which fitting seats 108 for fitting the cushion-fitting beam 31 are provided respectively on upper surfaces of the left arm portion 75 and the right arm portion 76, and the fitting seats 108 are provided with female screw portions 111, 111 for screwing the bolts 77 (See Fig. 3).

[0034] Action or effects of the rear suspension structure described above will be described below.
   Fig. 7 is a first action view for illustrating the action or effects of the rear suspension structure according to the present invention.
   When the swing arm side fitting portion 61 of the rear cushion unit 28 is fitted to the swing arm 24 through the cushion-fitting beam 31, the cushion-fitting beam 31 closes a part of the window portion 106 of the swing arm 24. Therefore, by fitting the cushion-fitting beam 31 to the swing arm 24, the rigidity of the surroundings of the window portion 106 provided for passing the rear cushion unit 28 therethrough is enhanced, and, accordingly, the flexural rigidity and torsional rigidity of the swing arm 24 as a whole can be enhanced.

[0035] As has been described referring to Fig. 2 and Fig. 7 above, the present invention is firstly characterized in that, in a rear suspension structure including the swing arm 24 having one end swingably fitted to the pivot shaft 25 provided on the pivot brackets 13, 13, the rear wheel 26 (See Fig. 1) fitted to the other end of the swing arm 24, and the rear cushion unit 28 having the swing arm side fitting portion 61 fitted to the swing arm 24, the link side fitting portion 62 of the rear cushion unit 28 being connected to the pivot brackets 13, 13 through a link mechanism included of the first link 32 and the second link 34, the left arm portion 75 and the right arm portion 76 extending in the front-rear direction are provided on the left and right sides of the swing arm 24, the window portion 106 for passing the rear cushion unit 28 therethrough is provided between the left arm portion 75 and the right arm portion 76, the cushion-fitting beam 31 is bridgingly provided between the left arm portion 75 and the right arm portion 76, the swing arm side fitting portion 61 of the rear cushion unit 28 is fitted to the cushion-fitting beam 31, and the whole part of a part of the window portion 106 is closed with the cushion-fitting beam 31.

[0036] Since the whole part or a part of the window portion 106 of the swing arm 24 is closed with the cushion-fitting beam 31, the swing arm 24 can be reinforced by the cushion-fitting beam 31, so that the flexural rigidity and torsional rigidity of the swing arm 24 can be enhanced.

[0037] Since the cushion-fitting beam 31 as a fitting member for the rear cushion unit 28 functions also as a reinforcement member for the swing arm 24, it is unnecessary to specially fit a reinforcement member to the swing arm 24. Further, since the upper end of the rear cushion unit 28 is fitted to the swing arm 24 through the cushion-fitting beam 31, the upper portion cross pipe 302 and the bracket portion 304 provided on the vehicle body frame 300 shown in Fig. 10 according to the prior art are unnecessary in the present invention, so that an increase in weight can be restrained even though the cushion-fitting beam 31 is fitted to the swing arm 24.

[0038] Figs. 8(a) to (d) are second action views for illustrating the action or effects of the rear suspension structure according to the present invention, in which (a) and (c) shows comparative examples, and (b) and (d) show the embodiments of the present invention.
   In the comparative example of (a), a straight beam 203 is fitted to arm portions 201, 202 of a swing arm 200, and an upper portion fitting portion 205 of a cushion unit 204 is fitted to the beam 203. In this structure, when the cushion unit 204 extends, a downward force FL acts on the upper portion fitting portion 205 as indicated by arrow a, and flexural moments ML act on the beam 203 in the directions of arrow b and arrow c.
   Since the spacing L between the arm portion 201 and the arm portion 202 of the swing arm 200 is large, the flexural moments ML are much larger.

[0039] In the embodiment of (b), when the rear cushion unit 28 extends, a force FL acts on the swing arm side fitting portion 61 as indicated by arrow a, in the same manner as in (a), and compressive forces FC act on the inclined portions 31b, 31b of the cushion-fitting beam 31 in the directions of arrow e and arrow f.
   At this time, though flexural moments act on the base portions 31a, 31a and the cushion-fitting portion 31c of the cushion-fitting beam 31, the flexural moments are smaller than the flexural moments ML described in (a) because the horizontal portion is short.

[0040] In the comparative example of (c), when the cushion unit 204 contracts, an upward force FU acts on the upper portion fitting portion 205 as indicated by arrow h, and flexural moments MU act on the beam 203 in the directions of arrow j and arrow k.

[0041] In the embodiment of (d), when the rear cushion unit 28 contracts, a force FU acts on the swing arm side fitting portion 61 as indicated by arrow h, in the same manner as in (c), and tensile forces FT act on the inclined portions 31b, 31b of the cushion-fitting beam 31 in the directions of arrow m and arrow n.
   At this time, though flexural moments act on the base portions 31a, 31a and the cushion-fitting portion 31c of the cushion-fitting beam 31, the flexural moments are smaller than the flexural moments MU described in (c) because the horizontal portion is short.

[0042] Thus, in the embodiments described in (b) and (d) above, when vertical forces act on the cushion-fitting beam 31 due to extension or contraction of the rear cushion unit 28, the vertical forces can be supported roughly as a compressive force or a tensile force by the inclined portions 31b, 31b of the cushion-fitting beam 31.

[0043] As has been described referring to Figs. 2, 3 and 8 above, the present invention is secondly characterized in that the cushion-fitting beam 31 is trapezoid shaped in front view, and the swing arm side fitting portion 61 of the rear cushion unit 28 is fitted to the cushion-fitting portion 31c of the cushion-fitting beam 31.

[0044] With the cushion-fitting beam 31 trapezoid shaped in front view, when vertical forces are exerted on the cushion-fitting beam 31 due to extension or contraction of the rear cushion unit 28, the vertical forces can be received roughly as a tensile force or a compressive force by the inclined portions 31b, 31b of the trapezoid-shaped cushion-fitting beam 31. For example, in the case where the beam is included of a straight member and the spacing between the left and right arm portions of the swing arm is wide, the horizontal portion of the beam is long and a much larger flexural moment is generated in the beam. In contrast, according to the present invention, the flexural moments can be reduced, and the rigidity of the cushion-fitting beam 31 against the extension and contraction of the rear cushion unit 28 can be enhanced.

[0045] Therefore, it is unnecessary to enlarge the cross sectional area of the cushion-fitting beam 31 or to specially reinforce the cushion-fitting beam 31, so that the weight of the cushion-fitting beam 31 can be reduced, and production costs of the cushion-fitting beam 31 and the rear suspension device 15 (See Fig. 1) can be reduced.

[0046] In addition, with the cushion-fitting beam 31 trapezoid shaped, the overall length of the rear cushion unit 28 can be enlarged, and a stroke amount required for the rear cushion unit 28 can be easily secured.

[0047] Further, with the cushion-fitting beam 31 screw-connected to the swing arm side fitting portion 61 of the rear cushion unit 28, the vertical fitting pitch of the rear cushion unit 28 can be easily changed by rotating the swing arm side fitting portion 61, so that adjustment of the vehicle height can be performed speedily and easily.

[0048] Fig. 9 is a third action view for illustrating the action or effects of the rear suspension structure according to the present invention.
   For example, where the rear cushion unit 28 is inclined relative to a normal fitting position (here, the normal fitting position of the rear cushion unit 28 is represented by a cylinder axis 120 of the rear cushion unit 28 fitted) by an angle θ (the actual angle θ is very small, but here it is exaggerated for convenience of illustration) due to, for example, torsion of the vehicle body during running or due to an error in mounting, the inclination of the rear cushion unit 28 can be absorbed by the spherical sliding bearing 93 at the swing arm side fitting portion 61 and the spherical sliding bearing 101 a the link side fitting portion 62.

[0049] As has been described above, the present invention is characterized in that the fitting of the swing arm fitting portion 61 of the rear cushion unit 28 and the fitting of the link side fitting portion 62 of the rear cushion unit 28 to the side of the pivot brackets 13, 13 are performed respectively through the spherical sliding bearings 93, 101.

[0050] The fitting of the swing arm side fitting portion 61 and the link side fitting portion 62 of the rear cushion unit 28 is performed through the spherical sliding bearings 93, 101, whereby the inclination of the rear cushion unit 28 relative to. the swing arm 24 side and the first link 32 side can be absorbed, and excessive external forces can be prevented from acting on the rear cushion unit 28 itself, the swing arm 24, the cushion-fitting beam 31, the first link 32, the second link 34 (See Fig. 2), the pivot brackets 13, 13 (See Fig. 2) or the like.

[0051] In the technology shown in Fig. 10 according to the prior art, when the upper end of the rear cushion unit 306 is fitted to a bracket portion 304 by, for example, a bolt-nut combination, upon inclination of the rear cushion unit 306 relative to the swing arm 308 in the vehicle width direction, the inclination cannot be absorbed, so that excessive external forces would be exerted on the rear cushion unit 306 itself, the bracket portion 304 and the upper portion cross pipe 302, and deflection or deformation would be generated, which is undesirable in view of durability.

[0052] In contrast, according to the present invention, the rear cushion unit 28 is rationally and easily inclined relative to the swing arm 24 side and the first link 32 side due to the presence of the spherical sliding bearings 93, 101, so that there is no problem as to durability of each of the above-mentioned portions, and not only the inclination in the vehicle width direction but also inclinations in any direction can be absorbed freely.

[0053] While the cross beam has been described as being trapezoid shaped in the present invention, the shape of the cross beam is not limited to this, and the cross beam may be in the shape of an upwardly convex arch in front view.
   In addition, while the upper end of the cushion unit has been fitted to the swing arm through the spherical sliding bearing in the present invention, the structure is not limited to this, and a side surface of a cylinder portion of the cushion unit may be fitted to the swing arm through a spherical sliding bearing. More in concrete, a structure may be adopted in which an inner ring of a spherical sliding bearing is fitted to the side surface of the cylinder portion of the cushion unit by screw connection or the like and an outer ring of the spherical sliding bearing is fitted to the swing arm. With such a structure, the vertical fitting pitch of the cushion unit can be shortened, and the inclination of the cushion unit relative to the swing arm can be absorbed.

[0054] Further, while the axis of the inner ring is parallel to or coincides with the cylinder axis of the cushion unit in the spherical sliding bearing on the upper end side of the cushion unit in the embodiment of the present invention, the structure is not limited to this, and the axis of the inner ring may be orthogonal to the cylinder axis of the cushion unit.
   Furthermore, the spherical sliding bearing in the present invention may be of an oiled type or a non-oiled type. Particularly, the non-oiled type is advantageous on the basis of maintenance.

[0055] A left arm portion 75 and a right arm portion 76 which extend in the front-rear direction are provided on the left and right sides of a swing arm 24, a window portion 106 for passing a rear cushion unit 28 therethrough is provided between the left arm portion 75 and the right arm portion 76, a cushion-fitting beam 31 is bridgingly provided between the left arm portion 75 and the right arm portion 76, a swing arm side fitting portion 61 of the rear cushion unit 28 is fitted to the cushion-fitting beam 31, and the whole part or a part of the window portion 106 is closed with the cushion-fitting beam 31.
   The swing arm can be reinforced with the cushion-fitting beam, and the flexural rigidity and torsional rigidity of the swing arm can be enhanced. Moreover, since the upper end of the cushion unit is fitted to the swing arm side, it is unnecessary to provide, for example, a fitting portion for the upper end of the cushion unit on the vehicle body frame side, so that an increase in weight can be restrained.

Claims

1. A rear suspension structure for motorcycle (10), comprising a swing arm (24) having one end swingably fitted to a pivot shaft (25) provided on the vehicle body side (13), a wheel (26) fitted to the other end of said swing arm (24), and a cushion unit (28) having an upper end (61) fitted to said swing arm (24), the lower end (62) of said cushion unit (28) connected to the vehicle body side (13), wherein
arm portions (75, 76) extending in the front-rear direction are provided on the left and right sides of said swing arm (24), a window portion (106) for passing said cushion unit (28) therethrough is provided between said arm portions (75, 76), a cross beam (31) is bridgingly provided between said arm portions (75, 76), said upper end (61) of said cushion unit (28) is fitted to said cross beam (31), and the whole part or a part of said window portion (106) is closed with said cross beam (31).

2. A rear suspension structure for motorcycle (10) as set forth in claim 1, wherein said cross beam (31) is trapezoid shaped in front view, and said upper end (61) of said cushion unit (28) is fitted to the upper side (31c) of said cross beam (31).

3. A rear suspension structure for motorcycle (10) as set forth in claim 1 or 2, wherein the fitting of said upper end (61) of said cushion unit (28) to said swing arm (24) and the fitting of said lower end (62) of a rear cushion unit (28) to the vehicle body side (13) are performed respectively through spherical sliding bearings (93, 101).

Drawing